Method of forming a multipart plastic structure



Dec. 29, 1953 E. DANIELSON ETAL 2,653,910

METHOD OF FORMING A MULTIPART PLASTIC STRUCTURE Filed July 6, 1951 2Sheets-Sheet l 3 TL. LI 1?. E

% a a W2 INVENTORS ELMEF? L. DANIELSON FLOYD J- DoFsEN ATTORNEYS Dec.29, 1953 E. L. DANIELSON ETAL 2,663,910

METHOD OF FORMING A MULTIPART PLASTIC STRUCTURE Filed July 6, 1951 2Sheets-Sheet 2 INVENTORS E LMER DANlELSON FLOYD J DOFSEN BY ATTORNEYSPatented Dec. 29, 1953 METHOD OF FORMING A MULTIPART PLASTIC STRUCTUREElmer L. Danielson, San Francisco,

Oakland, and Floyd J Dofscn, Galif., assignors to Elmer L.

Danielson and Floyd J. Dofsen, as joint tenants.

Application July 6, 1951, Serial No. 235,416 Claims. (Cl. 18-59) Thepresent invention relates to an improved method of forming a multi-partplastic structure, and it consists of the steps of the methodhereinafter described and claimed. 7

This application embodies steps which are inherent in our followingcopending cases, but are treated herein as constituting a separateinvention: (a) Method for Forming a Composite Plastic Structure, SerialNo. 203,992, filed January 2, 1951, now Patent No. 2,607,957, datedAugust 26, 1952; and (b) Method for Forming a Multi-Part PlasticArticle, Serial No. 207,174, filed January 22, 1951, now Patent No.2,609,570, dated September 9, 1952,

Generally speaking, we provide a precast plastic part having acharacter-defining slot extending therethrough, and this part is made ina selected color. Thereafter, a second plastic part is cast in acontrasting color so as to provide a character in the slot of the firstpart, and with the two parts bonded together into a unitary structure.It is particularly important this second casting be accomplished withoutallowing the material for the second part to flash over that face of theprecast part that normally will be exposed to view of an individual inthe final structure.

More specifically stated, we precast the first plastic part withprojections extending from a rear face thereof against which a secondplastic part is to be cast, and further having a characterdefining slotextending between the rear and front faces of the precast part.Subsequently, the precast part is placed in the cavity of a mold die,with the projections extending toward the mouth of the cavity, and thefront surface of the precast part abutting a supporting wall definingthe bottom of the cavity.

There'upon, a second mold die is brought into coacting relation with thefirst to close the cavity, while utilizing the second die to applypressure upon the projections to move and hold the front face of theprecast part into intimate contact with the supporting wall to preventthe material for the second part from flashing therebetween. Uponinjecting the material for the second part under heat and pressure intothe unoccupied space of the cavity, the character is produced in theslot.

Moreover the injection of the material for the second part isaccomplished so as to bond the two parts together into a unitarystructure.

Other objects and advantages will appear as the specification continues,and the novel features of the invention will be set forth in the claimshereunto appended.

Drawings For a better understanding of our invention, reference shouldbe had to the accompanying drawings, forming part of this application,in which:

Figure 1 is a rear view of a precast plastic part, illustrating acharacter-defining slot extending therethrough, and a series ofprojections extending therefrom; 7

Figure 2 is a vertical sectional view taken along the plane II-II ofFigure 1;

Figure 3 is a sectional view disclosing the precast part disposed in thecavity of a mold die, and a second die coacting with the first to closethe cavity and bearing against the projections to hold the front face ofthe precast part against the bottom wall of the cavity;

Figure 4 is a view corresponding to Figure 3, but disclosing the plasticmaterial for the second part injected into the unoccupied space of thedie cavity;

Figure 5 is a front face view of the final structure; and I Figure 6 isa vertical sectional the plane VI--VI of Figure 5 While we have shownonly one embodiment of our invention, it should be understood thatvarious changes, or modifications, may be made within the scope of theannexed claims without departing from the spirit thereof.

Detailed description Referring now to the drawings in detail, we show aprecast first part indicated generally at A, which may be made fromsuitable thermoplastic material in a selected color. This precast parthas front and rear faces [0 and H, respectively, having acharacter-defining slot 12 extending between these faces. Moreover, aplurality of projections i4 and Ma, are provided on the rear face I I ofthis part so as to extend therefrom.

Although the numeral 5 has been selected for the purpose of illustratinga slot, the term character is sufficiently generic to include anydiscriininating mark, sign, letter, symbol or design.

As illustrated in the drawings, the precast part A includes anannularwall I5. However, we do not wish to be limited in this respect.Our final structures may be key caps for calculators or typewriters,telephone dials, stove knobs, clock faces, etc. Such structures arementioned by way of disclosing various items that may be made byemploying our method.

Turning to Figure 8, we have shown a lower mold die B as being providedwith a cavity 18 view taken along 3 therein. This cavity is designed toreceive and support the precast part A, with the front face In of thelatter resting on the bottom wall II of the cavity. This wall conformsto and provides a barrier forming a flush closure over the slot I2 atthe front face ID of the precast part.

After the precast part A has-been disposed in the cavity of the lowerdie mold, with the projections I I-45a extending upwardly toward themouth or open top of the cavity I6, an upper mold die C is moved intocoacting relation with the lower die to close the mold cavity. As'clearly shown in Figure 3, the upper die has a core I8 extendingdownwardly into the cavity it upon closing the mold.

This core is adapted to bear'against the projections I l to applydownward pressure upon the latter, and thus moving and holding the frontface In of the precast part A in intimate contact with the supportingbottom wall ll of the die cavity. It will be observed that the core isgrooved at I9, or otherwise shaped, so as not to bear against theprojections I ia for the purpose to be set forth later.

Now a thermoplastic plastic material for a second part D is injectedthrough a channel 26 so as to fill the unoccupied space of the moldcavity. This material has a color contrasting with the part A and willfill the slot I2, as shown in Figure 4, providing a character hereinshown as the numeral 5. This character will be viewable from the frontface It in the final structure (see Figures 5 and 6).

The intimate contacting relation maintained between the front face ID ofthe precast part A I and the bottom wall II of the mold cavity willprevent any flashing therebetween during the injection of the secondplastic material. This is an important feature of our invention.

It will be noted that the second part D is cast to provide a backing onthe rear face II of the precast part, which is formed integral with thecharacter 5. This backing extends around and embeds the projections I4.The groove is provides ample room in the die cavity to form a filletlikerim 2| on the second part D that merges into the annular wall I5 of theprecast part. Also, this rim embeds and concealsthe projections I ia(see Figure 6).

The thermoplastic material for the second part D is injected underpressure and temperature. The range of temperature employed is such thatthe marginal portions of the projections I4I4a will soften so that thefirst and second parts A and D, respectively, will bond together into a,unitary structure. However, this temperature is controlled to the pointthat the remaining unsoftened portions of the projections It will havesufficient rigidity for transmitting force from the second die 0 tomaintain the front face In of the precast part against the bottom wallll of the mold cavity.

In this connection, we wish to point out the fact that relatively largeprojections I l would absorb the heat without softening the marginalportions thereof. On the other hand, very small projections would meltaway during the injection of the second material, and thus the upper dieno longer would. force the front face I0 of the precast part downagainst thebottom wall I? of the die cavity. Accordingly, a criticalrange exists for the proper sizes of the projections, depending upon thetemperature and pressure employed and the distance they are spaced fromthe point where the second plastic enters the mold.

After the proper cooling time has elapsed, the dies B-C are opened, andthe composite plastic structure A-D removed. The sprue 22 may be snappedoff readily, since it is not desired in the final structure. Theprojections Ida are shown in Figure 2 as being of the same height as theprojections Ida In certaincases, the projections Ida could be "shorterthan the other projections It and thus be embedded in the secondplastic.

We claim:

1. In the herein described method of forming a multipart plasticstructure, the steps of: precasting a first plastic part with aplurality of individual spaced-apart projections extending from a rearface thereof; said face being adapted to havea second plastic part castthereagainst; this precast part being provided with a characterdefiningslot extending therethrough from its rear face to an opposing frontface; butting the front face of the precast part against a supportingwall to provide a barrier over the slot at the iront face of this part;applying pressure against the projections in a direction to move andhold the front face of the precast part in intimate contact with thesupporting wall; and injecting material for a second plastic part underheat and force against said rear face of the precast part to fill thespaces among the projections, with said material surrounding andembedding the projections; the temperature of the injected materialbeing sumcient to bond the two plastic parts into a unitary structure;said material further filling the slot to provide a character thereinviewable from the front face of the precast part in the final structure;the injecting of the material for the second part being accomplishedwhile maintaining the pressure on the projections to thereby retain thefront face of the precast part up against the supporting wall to preventthis material from flashing therebetween and marring the front face ofthe precast part, and further preventing said front face from yieldingaway from the supporting wall duringthe injecting of the material forthe second part.

2. The method as defined in claim 1, in which the temperature of theplastic material for the second part is sufficient to soften portions ofthe projections so that the first and second plastic parts will bebonded together, while leaving the remaining portions of the projectionssufficiently rigid for transmitting the pressure, when applied upon theprojections, to the front face of the precast part to thereby maintainthis face in intimate contact with the supporting wall.

3. The method as defined in claim 1, in which.

the projections are cast so as to be dispersed over an area entirelysurrounding the slot in the precast part to thereby effectively hold thefront face of this part against the supporting wall when the pressure isapplied to the projections in a direction toward said wall.

4. The method as defined in claim 1, in which at least some of theprojections are cast adjacent to the walls of the slot; to thus aid inpreventing the front face of the precast part, in the region of theslot, from yielding away from the supporting wall, while said pressureis maintained on the projections.

5. In the herein described method of forming a multipart plasticstructure, the steps of: precasting a first plastic part with aplurality of individual spacedapart projections extending from a rearface thereof; said face being adapted to have a second plastic part castthereagainst; thi precast part being providediwith a character- 5defining slot extending therethrough from its rear face to an opposingfront face; cutting the front face of the precast part against asupporting wall to provide a barrier over the slot at the front face ofthis part; applying pressure against certain of the projections in adirection to move and hold the front face of the precast part inintimate contact with the supporting Wall, the remaining projectionsbeing kept free of such pressure; and injecting material for a secondplastic part under heat and force against said rear face of the precastpart to fill the spaces among the projections, with said materialsurrounding and embedding the projections; the temperature of theinjected material being suificient to bond the two parts into a unitarystructure; said material entirely covering those projections notsubjected to said pressure; said material further filling the slot toprovide a character therein viewable from the front face of the precastpart in the final structure; the injecting of the material for thesecond part being accom plished While maintaining the pressure on theprojections to thereby retain the front face of the precast part upagainst the supporting wall to prevent this material from flashingtherebetween and marring the front face of the precast part, and furtherpreventing said front face from yielding away from the supporting Wallduring the injecting of the material for the second part.

ELMER L. DANIELSON. FLOYD J. DOFSEN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,120,553 Flader June 14, 1938 2,285,963 Grits June 9, 19422,298,365 Gits Oct. 13, 1942 2,350,787 Martin June 6, 194

